1. Field of the Invention
The present invention relates generally to hand trucks. More particularly, the invention concerns an improved hand truck having novel stair tread roller assembles which enable the user to easily move loads up and down stairs using the hand truck.
2. Discussion of the Prior Art
Hand trucks are not new and several variations thereof have been used over the years to move heavy loads from place to place. However, the conventional hand truck is not well suited for moving loads up and down stairs. Accordingly, a number of hand truck designs have been suggested to alleviate this problem. Typically these prior art designs involve the addition to the conventional hand truck of stair tread engaging devices which facilitate movement of the hand truck on stairways.
Exemplary of a prior art hand truck design having stair tread engaging devices is that disclosed in U.S. Pat. No. 4,290,618 issued to Morton. The Morton device comprises a hand truck to which a pair of specially designed stair tread engaging roller assemblies have been added. These roller assemblies include an endless V-belt which rides along a plurality of barrel shaped rollers having flat end walls and a bulging side wall. Each of the rollers is mounted in an individual cavity in the device frame and is rotatable within the cavity about its own axis. The rollers are generally linearly aligned and are non-linearly movable with respect to the frame. The tread engaging device further includes flanges for maintaining the V-belt on the device.
Another useful prior art hand truck device is that disclosed in U.S. Pat. No. 5,253,881 issued to Dunkle. Like the Morton device, the Dunkle hand truck includes a pair of stair crawler assemblies which are mounted on the side frames of the hand truck. Each of the crawler assemblies includes a pair of spaced apart bearing retainer plates between which a plurality of roller bearings are mounted. The roller bearings collectively support an endless belt member which engages the stair treads.
Other prior art devices which embody stair tread engaging devices are described in U.S. Pat. No. 2,193,283 issued to Harberson; U.S. Pat. No. 2,301,341 issued to Stevens et al and U.S. Pat. No. 4,136,888 issued to Bowie, Jr. et al.
A major drawback of many of the prior art hand trucks with stair tread engaging devices resides in the fact that because of the design of the stair tread engaging assemblies considerable friction is created tending to impede smooth and free movement of the tread engaging belts relative to the frame of the assembly about which the belt is entrained. For example, in certain of the prior art devices in which the rollers rotate in cavities, the end walls of the rollers frictionally engage the side walls of the cavities within which the rollers rotate. Also, during operation of certain of the prior art devices, the stair tread engaging belts have a tendency to rub against the side walls of the frame about which they are entrained causing further friction. In other prior art devices in which the belt supporting rollers are not individually rotatably supported by the axles the rollers tend to engage their adjacent rollers causing additional friction build-up.
It is the foregoing and various other drawbacks of the prior art which the present invention seeks to overcome by providing an apparatus which is constructed in a manner to effectively prevent friction buildup. More particularly, this is uniquely achieved by providing properly designed, individually mounted, freely rotatable belt supporting rollers and properly designed supporting frames which effectively guide the belts into engagement with the rollers without frictionally engaging the sides of the supporting frames. In this way, an easy-to-use, minimum friction and smoothly operating apparatus is provided which permits relatively friction free movement of the stair tread engaging belts about the supporting frame of the device.